This invention is in the field of artificial horizon devices which project a line of light or light bar onto a surface in front of a pilot. The position and attitude of the light bar is controlled in order to simulate the true horizon. Aircraft, including helicopters, and other craft which move in three dimensions, as well as flight simulators, may include such a device to assist the pilot in controlling the craft.
Conventional aircraft instruments include an artificial horizon instrument which indicates the orientation of the aircraft relative to a horizon. This instrument is generally located on the aircraft instrument panel directly in front of the pilot. When the true horizon is not visible to the pilot the artificial horizon device may be inspected occasionally by the pilot in order to determine the attitude of the aircraft. Such an inspection requires the pilot to use central vision which encompasses a solid angle of about 3 degrees in the center of the visual field. A conventional artificial horizon device in addition to requiring the use of central vision presents only a symbol to the pilot. Such a symbol requires correct perception, decoding, and interpretation before any sense of spatial orientation or motion can be obtained.
On the other hand, peripheral vision is used naturally for sensing orientation and motion. Peripheral vision utilizes dedicated cerberal faculties which recognize line-like features in the peripheral vision field. Details about the relative movements and positions of these features are conveyed to the center of the brain responsible for motion perception. This inherent perceptual function of the human brain is carried on continuously and automatically during consciousness and requires no conscious thought. Thus, any instrument which provides information about attitude and movement through the peripheral vision field will make use of the dedicated faculties and free the pilot's conscious thinking and analytical abilities for other uses.
Because it is not practical to increase the size of conventional artificial horizon instruments so they can be viewed in the peripheral vision field, devices have been developed which project a line of light or light bar onto the aircraft instrument panel in front of the pilot. The light bar is moved on the instrument panel by the device to indicate the position of the true horizon.
One approach to providing a line of light or light bar in front of the pilot and observable by the peripheral vision is to be found in U.S. Pat. No. 4,083,239. A light source is mounted in a housing and one part of the housing is made to tilt and another to rotate thereby moving optical elements which combine to transmit a light bar in front of the pilot. Movement of the parts is related to the aircraft's gyro platform so that the light bar gives a display representing the true horizon at all times. Although this structure is acceptable in some applications, it is not practical in all aircraft primarily because the structure is quite bulky and will not fit readily into the cockpit of existing aircraft. The structure also suffers from the inherent disadvantage concomitant with movement of relatively large mechanical parts in conditions of extreme temperature or acceleration forces. Such disadvantages compromise the use of the device in aircraft such as fighters.